Lot depends on the state you live in, and the agency you are working with and the people how run the agency.
Some pitfalls would be HUD would become your business partner; You have to use their paperwork or lease; lease would most likely be for a year; The monthly rate they will pay may be lower that market rate; you will have to screen them the same as everyone else; the tenant may not have the skills necessary to understand how work with you on keep the property in good condition, relying on the service to catch and report things that need to be fixed; your property will have to meet a certain standard of acceptance and you will be required to keep it at that standard and do it in a certain time frame.
For example. I have a property that the living room windows have never been opened. It's been rented for 15 year without one single person asking for a window screen for this window. Section 8 family wants to rent, ok, I run credit report, she likes the place, I like her too... HUD does their inspection, they require window screens on all windows,,, however it was fine for the last 15 years for people who were not section 8... so I don't rent to this family because I'm not going to put a window screen on that window! Now another 15 years later and there is still no screen and no one minds! Matter of fact, they like looking at the woods and the birds without looking thru a screen.
There are good things to write about renting to section8 but that is not the question! Learn your state and county laws regarding section 8, visit the office, meet the people who will become your business partners if you go this route. Sometime a person lives in a community where the offices are fairly run, other times beware. Talk to other LL in your area who deal with these agencies. Join networking clubs and educate yourself and screen these people just like you would anyone else. It's a great program for those who need it and LL's who are fortunate to live in an area where it's run by decent folks.
Rent on!